Monolithic integrated structure including fabrication thereof

ABSTRACT

THIS INVENTION RELATES GENERALLY TO MONOLITHIC INTEGRATED STRUCTURES INCLUDING THE FABRICATION THEREOF AND, MORE PARTICULARLY, TO A MONOLITHIC INTEGRATED STRUCTURE THAT IS USED TO PROVIDE A MULTIPLICITY OF VARIOUS CIRCUIT INTERCONNECTIONS SO AS TO PERMIT MORE THAN ONE CIRCUIT TO BE MADE FOR EACH STRUCTURE. MANY LOGIC TYPE INTEGRATED STRUCTURES CAN BE FABRICATED FROM A SINGLE MASTER SLICE CONFIGURATION WHICH CONTAINS A NUMBER OF COMPONENTS IN A PATTERN FAVORABLE TO THE FORMATION OF ANY SELECTED LOGIC CIRCUIT FROM A CLASS OF MANY SUCH CIRCUITS. ADDITIONALLY, FABRICATION TECHNIQUES ARE DESCRIBED FOR FACILITATING FORMATION OF THE INTEGRATED CHIP WHICH INCLUDE MASK ALIGNMENT TECHNIQUES, CHIP TESTING TECHNIQUES, CHIP IDENTIFICATION, PROCESS STEP IDENTIFICATION, ENGINEERING CHANGE NUMBER IDENTIFICATION, ETC.

Oct. 10, 1972 Original Filed May 23, 1967 FORM SEMICONDUCTOR WAFER OF P' TYPE CONDUCTIVITY OXIDIZE WAFER SURFACE MASK AND ETCH HOLES IN OXIDE LAYER (MASK-A) FORM N REGIONS IN THE WAFER SURFACE BY DIFFUSION OXIDIZE WAFER SURFACE To CREATE DEPRESSION ABOVE N REeIoNs I L REMovE OXIDE LAYER I I EPITAXIALLY GROW A LAYER OF N TYPE MATERIAL (2N THE WAFER SURFACE AND ON THE N REGIONS OXIDIZE SURFACE OF EPITAXIALLYQ GROWN LAYER MASK AND ETCH A NETWORK OF CHANNELS IN THE OXIDE LAYER EXPOSING THE SEMI- coNDucToR SURFACE (MASK a DIFFUSE P TYPE ISOLATION REGIONS I. FEINBERG HAL MONOLITHIC INTEGRATED STRUCTURE INCLUDING FABRICATION THEREOF REOXIDIZE WAFER SURFACE MASK AND ETCH HOLES IN OXIDE LAYER ABOVE EPITAXIALLY GROWN REGIONS (MASK C) I DIFFUSE P TYPE BASE AND RESISTOR REGIONS INTO ISOLATED N TYPE EPITAXIALLY GROWN REGIONS OXIDIZE SURFACE AND DRIVE IN IMPURITIES FORMING THE BASE AND RESISTOR REGIONS MASK AND ETCH HOLES IN OXIDE LAYER ABOVE BASE REGIONS AND 2R AND 3R RESISTOR REGIONS(MASK-D) FIG.

17 Sheets-Sheet 1 DIFFUSE IN N TYPE IMPURITIES TO FORM EMITTER REGIONS AND ALSO TO FORM N REGIONS FOR 2R AND 3R RESISTORS DRIVE IN IMPURITIES FORMING THE EMITTER REGIONS FORM OPENINGS IN FIRST PHOTO RESIST LAYER FOR MAKING CONTACT TO DESIRED SEMICONDUCTOR REGIONS (MASK-EI v REPEAT PHOTOLITHOGRAPHIC MASK AND ETCHING OPERATION TO PREVENT PINHOLES IN OXIDE LAYER (MASK-E2) FORM METAL INTERCONNECTIONS AND OHMIC CONTACTS (MASK F) I I APPLY SPUTTERED OXIDE OVERCOAT MASK AND ETCH TERMINAL HOLES IN SPUTTERED OXIDE OVERCOAT LAYER (MASK c) I EVAPORATE CR, CU, AND AU INTO TERMINAL HOLES (MASK-H) EVAPORATE OVERSIZE PB-SN PADS oNTo CR, cu, AU LAND PORTIONS (MASK-I) I MELT PADS To REFLOW BACK To LANDs I ma WAFER INTO CHIPS J I APPLY MONOLITHIC INTEGRATED CHIPS oN PRINTED LAND PATTERNS oN CERAMIC SUBSTRATE INTERcoNNEcT MONOLITHIC INTERGRATED CHIPS TO PRINTED LAND PATTERN INVENTORS IRVING FEINBERG JACK LEE LANGDON CARL LEE sITIER M zlfli,

AGENT Oct. 10, 1972 l. FEINBERG ETAL 3,697,318

MONOLITHIC INTEGRATED STRUCTURE INCLUDING FABRICATION THEREOF Original Filed May 23, 1967 17 Sheets-Sheet 2 STEP 1 STEP 1 PFIG.

Oct. 10, 1972 FElNBERG ETAL MONOLITHIC INTEGRATED STRUCTURE INCLUDING FABRICATION THEREOF Original Filed May 23. 1967 17 Sheets-Sheet 5 TUL in;

I. FEINBERG ETAL 3,691,318 MONOLITHIC INTEGRATED STRUCTURE INCLUDING FABRICATION THEREOF l7 Sheets-Sheet 4 .Oct. 10, 1972 Original Filed May 23. 1967 FIG. FIG.

FIG. 4'

Oct. 10, 1972 FEINBERG ETAL MONOLITHIC INTEGRATED STRUCTURE INCLUDING FABRI CAT ION THEREOF l7 Sheets-Sheet 8 Original Filed May 23. 1967 FIG. 4B

lllL L Oct. 10, 1972 I. FEINBERG ETA!- 3,597,313

HQNOLITHIC INTEGRATED STRUCTURE INCLUDING FABRICATION THEREOF Original Filed May 23, 1967 17 Sheets-Sheet 6 FIG. 40

36T SOT 34T v 32T 30T Oct. 10, 1-972 1. FEINBERG ET MONOLITHIC INTEGRATED STRUCTURE INCLUDING FABRICATION THEREOF 7 Original Filed May 23. 1967 17 s t -s t 7 xEQwEE G:

8:2: EH22: 9a

Oct. 10, 1972 l. FEINBERG EI'AL 3,

HONOLITHIC INTEGRATED STRUCTURE INCLUDING FABRICATION THEREOF Original Filed May 25. 1.967 17 Sheets-Sheet 8 FIG FIG. 5A

illlll- I n A p r v FIIL lllli ||1L i h lllll w J m w 1 MK 8 L j m m W m 1 llll ll IL m 1 .U l W W F |1|L M W WW Oct. 10, 1 972 I. FEINBERG ETAL MONOLITHIC INTEGRATED STRUCTURE INCLUDING FABRICATION THEREOF Original Filed May 23. 1967 17 Sheets-Sheet 9 FIG. 5B

Och 10, 1972 FElNBERG ETAL NONOLITHIC INTEGRATED STRUCTURE INCLUDING FABRICATION THEREOF Original Filed May 23. 196? 1'7 Sheets=Sheet l0 5 imp? E52 Oct. 10, 1972 I FEINBERG ET AL 3,597,313

MONOLITHIC INTEGRATED STRUCTURE INCLUDING FABRICATION THEREOF 17 Sheets Sheet 11 Original Filed May 25. 1967 FIG.6' FIG. 6A

.L I I J I I I I I l L FIG. FIG. 6A 68 Oct. 10, 1972 I. FEINBERG HAL MONOLITHIC INTEGRATED STRUCTURE INCLUDING FABRICATION THEREOF l7 Sheets-Sheet 12 Original Filed May 23, 1967 FIG. 6B

T EST TRANSlSTOR TEST TRANSISTOR Oct. 10, 1972 l. FEINBERG ETAL MONOLITHIC INTEGRATED STRUCTURE INCLUDING Original Filed May 23, 1967 FABRICATION THEREOF l7 Sheets-Sheet 15 X ,I 2 I E ii- I? FIG.T

06- 0, 1972 I. FEINBERG ETA!- QNOLITHIC INTEGRATED STRUCTURE INCLUDING FABRICATION THEREOF l7 Sheets-Sheet 14 Original Filed May 25, 1967 OTQE m 0 271. MY? 5 Q: 02 Us I I I E 02 m n-n-n- .m m m QN ./QN a? m y. H H U n I I at ew HM-N ow 3p QQNLI II II a m 1 I Q2 3 Us 0 v6 32 0 v Oct; 10, 1972 l. FEINBERG EPA!- 3,597,313

MONOLIITHIC INTEGRATED STRUCTURE INCLUDING FABRICATION THEREOF Original Filed May 23, 1967 17 Sheets-Sheet l8 MASK E27 FIG. 12

I11 I l I II" II algl lml II II l l I I I I I III LU In l I II I l l 2 In l I In H I lull I I I In II II I l ||u| ||||l l I II: o l u "I" H N) MASK 51 FIG."

Oct. 10, 1972 FElNBERG ETAL 3,691,318

MONOLITHIC INTEGRATED STRUCTURE INCLUDING FKBRICATIOIW THEREOF Original Filed May 25, 1967 17 Sheets-Sheet 16 I 0 0 o E I w 52 I O 0 I 2 2 I r 0 3 0 s: I

PIC-3.13

United States Patent O 3,697,318 MONOLITHIC INTEGRATED STRUCTURE INCLUDING FABRICATION THEREOF Irving Feinberg, Poughkeepsie, and Jack L. Langdon and Carl L. Sitler, Wappingers Falls, N.Y., assignors to International Business Machines Corporation, Armonk,

Original application May 23, 1967, Ser. No. 640,610, now Patent No. 3,539,876, dated Nov. 10, 1970. Divided and this application Dec. 12, 1969, Ser. No. 889,807

Int. Cl. B44d H18; H01!) 13/00; Hk 3/00 US. Cl. 117--212 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates generally to monolithic integrated structures including the fabrication thereof and, more particularly, to a monolithic integrated structure that is used to provide a multiplicity of various circuit interconnections so as to permit more than one circuit to be made for each structure. Many logic type integrated ment techniques, chip testing techniques, chip identifica-' tion, process step identification, engineering change number identification, etc.

CROSS REFERENCES TO RELATED APPLICATIONS OR PATENTS This is a divisional application of co-pending US. patent application Ser. No. 640,610 filed on May 23, 1967, now U .S. Pat. No. 3,539,876, and assigned to the assignee of this application.

(1) Ser. No. 364,834, filed Feb. 24, 1964, now Pat. No. 3,321,441, investors, Fred Barson :and Walter E. Mutter.

(2) Ser. No. 376,066, filed June 18, 1964, now Pat. No. 3,343,049, inventors, Fred Barson and William H. Miller.

(3) Ser. No. 428,733, filed January 28, 1965, now Pat. No. 3,369,991, inventors, Peter D. Davidse and Leon I. Maissel.

(4) Ser. No. 465,034, Circuit Structure and Method, filed June 18, 1965, now Pat. No. 3,429,040, inventor, Lew Miller.

(5) Ser. No. 539,210, Monolithic Integrated Structure Including Fabrication and Package Therefor, filed Mar. 31, 1966, now Pat. No. 3,508,209, inventors, 'Benjamin Agusta et al.

(6) Ser. No. 606,939, Digital Circuit With Anti-Saturation Collector Load Network, filed Jan. 3, 1967, now Pat. No. 3,505,535, inventor, Joseph R.-Cavallere.

(7) Ser. No. 607,923, Method for Etching an Opening- BACKGROUND OF THE INVENTION (1) Field of the invention A This invention relates generally to monolithic semiconductor integrated structures including the fabrication thereof, and, more particularly, to monolithic integrated logic structures that can be readily mounted onto .a module for use in machines such as computers, etc.

3,697,318 Patented Oct. 10, 1972 (2) Description of the prior art Recently, the fabrication of monolithic integrated semiconductor circuits, preferably of silicon, has become more important in producing electronic equipment that requires, for competitive reasons, low cost integrated devices. The current trend in making integrated devices is to use the so-called planar technology wherein all diffusions are carried out on one surface of the semiconductor structure. In the manufacture of integrated devices using the planar technology, the master slice concept became important in permitting the fabrication of integrated circuits of many types from a single master slice. Problems were encountered in selecting the proper master slice configuration which would provide the flexibility desired for making a number of desired electrical circuits. The proper location of components became an important consideration. Furthermore, fabrication techniques were needed to permit proper identification of the integrated chip, the completed step in the process of making the integrated, chip, the dicing of the integrated chip, etc.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide an improved monolithic integrated structure.

It is a further object of this invention to provide an improved fabrication method for making monolithic integrated devices.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with one embodiment of this invention, a monolithic semiconductor master slice structure comprises a rnonocrysta-lline semiconductor substrate and spaced terminal pad areas located about the peripheral portion of the structure. An excess number of active and possive components are located in the area defined by the pad areas thereby permitting several integrated circuits to be fabricated from the master slice structure by selecting and interconnecting the desired active and passive components.

In accordance with another embodiment of this invention, a monolithic integrated semiconductor chip comprises a monocrystalline semiconductor substrate having spaced terminal pads located about the peripheral portion of the chip. Active and passive components are located in the semiconductor area defined by the terminal pads. Metal conductive paths electrically interconnect less than all of said active and passive components located in the arela defined by the terminal pads to specified terminal pa s.

In accordance with still another embodiment of this invention, a resistor for a monolithic integrated semiconductor chip comprises a substrate of one type conductivity. A low resistance region of the opposite type conductivity is located in the substrate and along one surface portion thereof. A high resistance region of the same conresistance region. A pair of spaced low resistivity regions is located in surface portions of the high resistance region. Each of the pair of spaced low resistivity regions is of the same conductivity type as the high resistance region and right angularly skewed with respect to the separated low resistance region. Ohmic contacts are provided tothe pair of spaced low resistivity regions.

In accordance with still another embodiment of this invention, a process for fabricating a monolithic integrated semiconductor chip includes the formation of spaced terminalpads in a parallel-sided configuration. Two adja-' cent spaced pads located on each side of two opposite making the monolithic integrated structure of the FIG. 6

parallel sides of'the chip are spaced further apart than the space between any other pair of adjacent pads. Metal H lized marks are formed 90 apart on at least one corner terminal pad for mask alignment purposes. Additionally metallized dicing mark indicators are formed adjacent the corner pads of the chip.

In accordance with another embodiment of this invention, a module. package for monolithic integrated semiconductor structures comprises a dielectric substrate. A conductive land pattern is formed on a surface of the dielectric substrate. A plurality of pins for module connection penetrates the dielectric substrate and connects to thelconductive land pattern. A monolithic integrated semiconductor chip is spaced from the surface of the dielectric substrate by means of terminal pads which are connected to the lands. Each of the plurality of pins is electrically connected to a terminal pad of the chip.

For a more detailed description of the environment in which the presently disclosed techniques are useful, refers to the parent patent application from which US. Pat. 3,539,876 matured.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiments of the invention, as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a flow diagram of the entire fabrication proc-.

ess for making the monolithic integrated structure and interconnecting it to a conductive land pattern formed on a ceramic substrate;

FIG. 2 is a flow diagram, in cross section, depicting the steps in the process for fabricating each pad P of the integrated structure of FIGS. and 6;

FIG. 3 is a flow diagram, in cross section, showing the steps in the process for fabricating the semiconductor underpass conductor U of the master slice of FIG. 4 (FIGS. 4A, 4B);

FIG. 4 is a top view of one master slice embodiment of this invention illustrating the location of each component;

FIG. .4 is a diagrammatic representation illustrating FIG. 4A andFIG. 4B as left and right portions of FIG. 4;

FIG. 4A is an enlarged view of the left hand portion of FIG. 4;

FIG. 4B is an enlarged view of the right hand portion of FIG. 4;

FIG. 4D is an enlarged, fragmentary, sectional perspective view of the components that are used in the master slice of FIG. 4;

FIG. 5 is a top view of a metallizedpattern showing one way of connecting components of the master slice of FIG. 4 to provide a logic type integrated circuit structure as shown schematically in FIG. 1C;

FIG. 5' is a diagrammatical view, in box form, showing the interrelationship of FIGS. 5A and 5B which together form thecomposite metallized pattern of FIG. 5;

FIG. 5A is an enlarged view of the left hand portion of FIG. 5;

FIG. 5B is an enlarged view of the right hand portion of FIG. 5;

FIG. 6 is atop view of a metallized pattern showing another way of connecting components of the master slice of FIG. 5.

FIG. 6' is a diagrammatical view, in box form, showing the interrelationship of FIGS. 6A and 6B which together form the composite metallized master slice and configuration of FIG. 6;

FIG. 6A is an enlarged view of theleft hand portion of FIG. 6;

FIG. 6B is an enlarged view of the right hand portion of FIG. 6;

FIGS. 7, 8, 9, 10', 11, 12, 13, 14, and 16 are planar embodiment of this invention; and

" FIG. 17 is a fragmentary, exploded, perspective View of a portion of each mask of FIGS. 716 shown in an overlay arrangement.

TI-[E SPECIFICATION Fabrication method In discussing the semiconductor fabrication method, as illustrated by the flow diagram of FIG. 1, the usual terminology that is well known in the transistor field will be used. In discussing concentrations, references will be made to majority or minority carriers. By carriers is signified the free-holes or electrons which are responsible for the passage of current through a semiconductor material. "Majority carriers are used in reference to those carriers in the material under discussion, i.e. holes in P type material or electrons in N type material. By use of the terminology minority carriers it is intended to signify those carriers in the minority, i.e., holes in N type material or electrons in P type material. In the most common type of semiconductor materials used in present day transistor structure, carrier concentration is generally due tothe concentration of the significant impurity, that is, impurities which impart conductivity characteristics to extrinsic semiconductor materials.

Although for the purpose of describing this invention reference is made to a semiconductor configuration wherein a P type region is utilized as the substrate and subsequent semiconductor regions of the composite semiconductor structure are formed in the conductivity type described, it is readily apparent that the same regions that are referred to as being of one conductivity type can be of the opposite type conductivity and furthermore, some of the operations which are described as diffusion operations can be made by epitaxial. growth and some of the epitaxial growth regions can also be fabricated-by diffusion techniques.

A wafer of P type conductivity preferably having a resistivity of 10 to 20 ohms-centimeter and a thickness of about 10 mils is used as the starting substrate. The substrate is preferably va monocrystalline silicon structure which can be fabricated by conventional techniques such as by pulling a rod-shaped silicon semiconductor member from a meltcontaining the desired impurity concentration and then slicing the pulled member into a plurality of wafers. The. substrate preferably has a crystallographic orientation of about 2.5 off the- 111 plane in the direction of the 110 plane to minimize pattern shift or washout after epitaxial growth. An oxide coating preferably of silicon dioxide and preferably having a thickness of approximately 6000 angstrom units is either thermally grown or deposited by pyrolytic deposition.

Alternatively, an RF sputtering technique, as described in a patent application identified as Ser. No. 428,733, filed Jan. 28', 1965, in the names of Davidse and Maissel and assigned to the same assignee as this invention, can be used to form the silicon dioxide layer.

Using standard photolithographic masking and etching techniques a photoresist layer (not shown) is deposited onto the oxide layer located on the substrate surface. By using an appropriate mask (mask A as shown by FIG. 7) the photoresist layer serves as a mask to expose surface regions on the surface of the substrate by etching away the desired portions of the SiO layer with a buffered HF solution. The photoresist layer is then removed to perunit further processing.

.A diffusion operation is carried out to diifuse into the exposed surface portions of the substrate N+ type regions having a C of 2X10 cm." of N type majority carriers.-

The sheet resistance of the N+ regions is approximately 9.0 ohms per square, and the depth of each diffused region is approximately micro inches. The surface oxide layer serves as a diffusion mask to prevent the N+ diffusion operation from forming an N+ region across.

the entire surface of the substrate. Preferably, the diffusion operation is carried out in an evacuated quartz capsule using degenerate arsneic doped silicon powder. As an alternative variation, each N+ region can be formed by etching out regions in the P- type substrate and then subsequently epitaxially growing N+ regions thereby using an etch and refill technique.

After the N+ diffusion operation, an oxidation step is preferably performed which causes conversion of the N+ surface regions into oxide (more than the remainder of the oxide masked surface of the substrate) and thereby creates a depression on each N+ surface region to permit subsequent identification or location after epitaxial growth.

The oxide layer which is located on the entire surface of the substrate layer is removed with a buffered HF solution. A region of N type conductivity, preferably having a resistivity of 0.09 ohms per centimeter, is epitaxially grown on the surface of the substrate and over the depressed N+ surface regions. The epitaxial region is an arsenic doped layer approximately 5.5:.2 microns thick. The depressions or recesses designating the location of the N+ regions are now located on the surface of the epitaxial layer to facilitate subsequent photolithographic masking and etching operations. In actual device fabrication, the arsenic impurities in the N+ regions, which are now buried, out diffuse about one micron during the epitaxial deposition.

An oxide layer approximately 4000 angstrom units thick is formed on the surface of the epitaxially grown region either by the thermal oxidation process, by pyrolytic deposition, or by RF sputtering techniques.

An isolation pattern of channels are formed in the oxide layer by standard photolithographic masking and etching techniques using a photoresist layer as a mask and a buffered HF solution to remove the desired oxide portions. The mask used in conjunction with the photoresist layer is Mask B as shown in FIG. 8.

The structure is now prepared for the subsequent isolation diffusion operation. A P diffusion operation is now carried out, preferably using a boron source, to form isolating P+ regions and the P+ under pass region (see FIG. 10) in the N type epitaxially grown region. The P regions have a C (surface concentration) of 2.2)( cm.- and a sheet resistance of 2.5 ohms per square. It is evident that the P+ diffused regions have a low resistivity surface region which extends downwardly from the surface of the semiconductor structure and each P+ region extends continuously from the P type substrate region to the surface of the semiconductor structure. The depth of each P+ region is approximately 300 micro inches.

A reoxidation operation is now carried out and by using photolithographic masking and etching techniques (with mask C as shown in FIG. 9) holes are opened up in the oxide layer to permit a base or P-type diffusion. The P- type diffusion operation is carried out through the exposed semiconductor surface portions to form P-type base regions for each transistor T, P-type resistivity regions for each IR resistor, and the P regions for the U underpass conductor. Boron is preferably used as the P-type impurity source to form regions having a C of l l0 atoms per cm.' a sheet resistance of 150:5 ohms per square, and a depth of about 80 micro inches.

The P-type diffusion step is followed by a simultaneous reoxidation and drive-in operation. Another layer of Si0 is thereby grown on the substrate surface. During this heat treatment, the boron impurities are redistributed thereby increasing the junction depth and lowering the C A photoresist coating is applied over the thermally grown oxide layer and by photolithographic masking and etching operations (using mask D as shown in FIG. 10) openings are formed in this oxide layer to permit N+ emitter type regions (for each T transistor) to be formed by a subsequent diffusion operation, two -N+ contact regions for the collector of each T transistor, and N+ contact regions for the 2R and BK resistors. The two N+ contact regions for each collector of the T transistor reduces the series resistance of the collector, N+ emitter regions are formed in the P-type base region of each T transistor.

The N+ regions are preferably formed using a phosphorous impurity source. The N+ contact regions for the 2R resistors are located right angularly skewed with respect to narrow extension portions of the buried N subcollector region. The C is 2.5 X 10 the sheet resistance is 3.5 ohms per square, and the depth is approximately 71 microinches. A phosphosilicate glass layer is formed on the substrate surface due to the phosphorous diffusion operation. The base channel width of each T transistor is approximately 17 microinches due to push out of the base region after formation of the diffused emitter region. The emitter and base regions of each T transistor are formed over the buried N+ region to permit this region to act as a bured low resistivity subcollector.

A drive-in operation is carried out using a nitrogen atmosphere. The purpose of carrying out a drive-in operation in a non-oxidizing atmosphere such as nitrogen is to maintain a high ,8 for the transistor T. If desired, following the emitter drive-in operation, a sputtered glass layer can be deposited on the phosphosilicate glass layer to protect the phosphosilicate glass layer which is needed for stability purposes as described in copending US. patent application Ser. No. 376,066, inventors, William H. Miller and Fred Barson, filed June 18, 1964 and assigned to the same assignee of this invention. Contact holes are opened up in the oxide layer in selected areas thereof by using two photoresist layers and two successive photolithographic masking and etching techniques (one for each layer using mask E1 as shown in FIG. 11 on the first photoresist layer and Mask E2 as shown in FIG. 12 on the second photoresist layer). The advantages of such a masking and etching process where the second mask also acts as a block out mask is clearly set forth in FIG. 3 of a copending patent application entitled Method for Etching an Opening in an Insulating Layer Without Forming Pinholes Therein, filed Jan. 9, 1967, inventors, Fred Barson et al., and assigned to the same assignee of this invention. For example, thedimensions of the emitter contact hole is 0.7 x 0.2 mils, each base contact hole 0.2 x 1.0 mils, and each collector contact hole 0.5 x 1.4 mils.

A layer of aluminum or other suitable metal such as molybdenum is evaporated over the entire wafer surface and portions of this layer are etched away to produce the desired interconnection pattern. An evaporated layer of aluminum with a thickness of several thousand angstrom units is useful to permit the formation of an interconnecting conductive path between components to thereby form the desired integrated circuit. A layer of photoresist is then applied to the wafer, dried, exposed, developed, and fixed. The aluminum interconnections are formed by a subtractive etching operation (with Mask F as shown in FIG. 13) using a warm solution of H PO4+HNO +H O. The photoresist layer is stripped off and the wafer is cleaned and dried.

The wafers are sintered in a nitrogen atmosphere at a temperature of about 450 C. for a period of about 15 minutes to permit the aluminum to produce good ohmic contact to the contacted semiconductor regions of the wafer. Thus, ohmic contacts are formed to each of the components.

Subsequently, a sputtered or otherwise deposited insulating layer of Si0 or other form of glass material is formed on the entire wafer surface. This encapsulating layer is provided over the entire wafer surface after the 

